The present invention relates to the field of photographic illuminators, and more particularly to the field of microphotographic illumination systems including a pilot light and strobe light.
It is well known to employ illumination systems for microphotography. Typically, these take two forms: ring lights and fiber optic illuminators. In addition, illumination systems are well known for microscopy, and long exposures for photographic purposes have often been employed to make use of a single illumination mode light source. A combined pilot lamp and strobe single head fiber optic illuminator for photomicroscopy is described in Allen, U.S. Pat. No. 4,006,487, expressly incorporated herein by reference. A ring light is a device that encircles a camera lens to provide radially uniform illumination, generally producing a shadowless image. A ringlight setup is unsuitable for many types of work, and is generally unavailable for microscopy, for example due to spatial constraints. Further, ring lights do not provide for rear illumination of transparent or translucent samples.
Fiber optic illuminators serve three essential functions. First, they may filter infrared and ultraviolet rays and thus avoid heat load and UV degradation of the subject. Second, they allow versatile positioning of multiple, e.g., three, illumination heads, which may be positioned arbitrarily with respect to the subject, including behind it. Third, fiber optic illuminators are known which integrate both pilot lamp and flash lamp, allowing the same optical fibers to carry flash illumination for photographic exposure and pilot light illumination for modeling and light source positioning. A pilot light is thus a lower intensity illuminator designed for composing the image visually, using a different, lower intensity continuous output light source than the strobe flash. Thus, it is known to align the pilot lamp and flash lamp within an aperture of al fiber optic collector, so that both sets of rays impinge upon the same optical fibers, thus assuring illumination along the same axis. However, such known systems generally suffer from a deficiency in that the ratio of pilot lamp to flash illumination may vary between fiber optic pickups, and that the flash illumination itself may vary in color balance between pickups at various locations.
Existing fiber optic illuminators thus suffer from poor homogeneity of the light output, and variations in relative light intensity between the pilot illuminator and the flash, as well as between different color of illumination by heads within the system. Thus, significant experimentation is necessary for high quality images to compensate for the inconsistencies.
Traditional designs of studio or professional-type illuminators do not necessarily seek high optical efficiency. Thus, in order to provide a robust, flexible, reliable and consistent system, light output may be wasted. Thus, the cost of power, equipment, and replacement parts (e.g., bulbs) are considered secondary to functionality. In production environments, i.e., those where the task is cataloging, data acquisition, documentation, or otherwise taking a large number of images, pilot lighting is important to avoid loss of productivity due to multiple exposures in order to properly compose the image prior to final image acquisition. Further, for transient, unstable or moving subjects, flash illumination is essential to freeze the image. Thus, a dual illumination mode illuminator is essential in such environments.
In production environments, the illumination system typically provides substantial excess illumination capacity, anticipating waste. In fact, this waste is generally acceptable in many environments, but limits the use of the systems to studios and other controlled environments with sufficient resources. For example, with a 250 Watt halogen pilot lamp, the fiber optic illuminator system requires substantial air flow and cooling, and an insulated case or other barrier to prevent human burn hazard and overheating. The fan provided for cooling produces a steady noise, and with the required air flow passages it is difficult to muffle the noise made by strobe triggering. Portable battery operation is typically restricted because of the high power draw.
A known design for a fiber optic illumination system provides an attachment to a standard studio strobe with modeling lamp, described in Baliozian, U.S. Pat. No. 4,428,029, expressly incorporated herein by reference, wherein a set of fiber optic pickups are arrayed in front of the strobe with each pickup aligned facing toward both the strobe and modeling lamp. A mechanical barrier or shutter allows modulation of light to the set of pickups, while traditional optical components may be placed at each fiber optic head. Prior fiber optic illuminators with both pilot and strobe modes, including the aforementioned type, suffered low optical efficiency due to poor utilization of the light output both illumination sources. In other words, the fiber optic bundles were not arranged to capture a large percentage of the available light output, but rather to provide modular arrangement and simple design. Further, each fiber optic bundle was independent, and therefore critically dependent on the positioning and local variations in lamp output. Therefore, while the fiber optic bundles indeed carried both pilot and flash illumination, the efficiency was low, and the illumination intensity and color balance were non-uniform and unregulated.
Strobe light output is generally governed by the time-intensity product of the flash. The intensity, in turn, is governed by the voltage and current (power) delivered to the flash lamp. Typically, the energy for the flash lamp is stored in a capacitor prior to triggering. The static voltage across the capacitor is insufficient to ionize the xenon gas within the tube, so a substantially higher potential trigger pulse is provided to commence the flash cycle. The flash cycle can be terminated in two ways. First, the energy stored in the capacitor can be fully discharged, down to a voltage insufficient to maintain ionization of the gas in the flash tube, and thus until the flash lamp no longer sustains conduction, or a high voltage semiconductor or switch can terminate the current flow in advance of full discharge.
The color temperature of the flash lamp depends on a number of factors, but for a given lamp, the current flow generally correlates with the color temperature over the course of a flash cycle. Thus, using a switch to prematurely terminate the flash cycle at an arbitrary time before complete discharge to control intensity will also have the undesired effect of changing the average color temperature of the lamp output over the flash cycle, since as the capacitor discharges, the voltage will drop and therefore the current through the lamp will drop over time. Using a single capacitor, complete discharge does not provide an efficient control over intensity, and therefore, a controllable shutter, iris or neutral density filter would be necessary to modulate output without changing color balance. This problem is compounded by known strobe drive systems that employ a rheostat (variable resistor) to control flash output; with each different setting of the rheostat, a different color temperature output would be expected due to the change in current through the lamp.
Therefore, advanced designs were developed to provide a plurality of capacitors within the strobe power pack, which are selected based on the desired output intensity. Thus, instead of seeking to drive the flash lamp over one or more orders of magnitude using pulse width intensity modulation, by cutoff timing alone, an appropriate capacitance and charge voltage is selected to normalize the starting and ending voltage on the flash lamp over the course of the cycle, and therefore impliedly normalizing the current and color temperature. So-called studio strobe power pack systems may therefore provide one or more capacitors (e.g., two), each of which may be charged to produce a predetermined power, e.g., 125, 250 or 500, Watt-seconds, and employed individually or in parallel (e.g., up to 1000 Watt-seconds, total), to power one to four heads. Such a design is incorporated in the M1000E power pack from Dyna-Lite, Hillside. N.J. Thus, the voltage and stored charge may be varied to alter illumination intensity, without altering output impedance. It is note that in such systems, the desired light output range must be set in advance. Fine adjustment of exposure is therefore effected by optical filters, variable apertures (irises), or the like.
Another known modulation system, typically employed in types of mobile strobe systems, provides for a series of mini-strobe pulses, which sum to the desired illumination. This method, while efficient, may result in change in color balance because the available power supply is unable to commence each pulse with a fully charged capacitor, especially for long duration flash cycles, due to increasing battery source impedance. Even high voltage battery supplies for strobes require the flash capacitor, due to the relatively high source impedance of the battery as compared to the capacitor.
Thus, the prior art has sought to provide strobe photographic illuminators with modeling lights having balanced ratio modeling illumination and accurate color balance, without meeting each of the objectives described herein.
The present invention provides a fiber optic illumination system which, in a first embodiment, provides excellent uniformity of illumination between lighting heads and between pilot and flash modes in both color and light output.
According to one embodiment, a fiber randomizer is preferably provided to evenly distribute light between respectively varying sources and destinations.
In a second embodiment, a single high power halogen pilot lamp is replaced with one or more metal vapor or fluorescent lamps. In this case, the pilot lamp color may vary substantially from a typical 3700 C for a halogen incandescent bulb. However, the color balance of the pilot lamp is generally not critical, so long as the object is visible and the lighting intensity closely approximates the flash in distribution and proportion. This improvement provides a lower power, higher efficiency, longer life pilot illuminator.
In a third embodiment, a common strobe lamp is provided for each fiber optic head, with a plurality of pilot lights being separated from the strobe, and the optical fibers carrying the pilot illumination are interspersed with optical fibers carrying the strobe. Alternately, the one type of light may enter the fiber from an end, while the other may enter through a side wall, thus providing a common pathway for both light sources.
In a fourth embodiment, a common strobe is provided for each fiber optic head, with separate pilot illuminators, each pilot illuminator being normalized in output to provide fixed ratio illumination between the respective strobe and pilot.
In a fifth embodiment, each fiber optic head includes a separate flash lamp and pilot illuminator, with a system for normalizing the output of each head.
A preferable embodiment of the present illumination system was designed to facilitate the proper lighting conditions to enable top quality color photographs of small objects in either micro or macro photographic conditions. This unit has been employed in conjunction with many types of cameras, lenses and microscopes with excellent results. This unit was primarily designed for use with high-resolution digital cameras, although it is suitable for all types of photography. Digital cameras are sensitive to Infra red light and in many cases employ a filter over the lens or CCD chip, to avoid IR contamination. The present illumination system eliminates the need for such a filter, thus increasing the overall throughput of the lens. A preferred embodiment employs efficient means to gather and transmit light to a specific point, with the use of fiber optic conduits. The light output is preferably controlled in at least two ways, neither of which change the light color temperature. Primary control is achieved with a capacitor discharge power pack system top control strobe operation. Secondary control is achieved through the use of mechanical irises, in-line with the fiber optic conduit. The light delivered to the subject is a cold light, ideal for heat sensitive subject matter. The preferred embodiment is a self contained unit and is not reliant on any specific camera lens or microscope.
Preferably, the system has a plurality of illumination heads, e.g., three heads, which are independently targetable toward the object to be illuminated. Therefore, illumination from various positions simultaneously is possible. In one embodiment, a single illuminator having strobe and pilot modes is provided which is adapted to be used with other illuminators to provide a predetermined precise pilot to strobe intensity ratio over a range of strobe output levels.
Typically, it is desired to turn off or block the pilot illumination during exposure, to ensure that the strobe color balance is preserved. In the case of an incandescent bulb pilot lamp, this requires a brief shutdown (cool-off) period, for example up to 5 seconds. Incandescent bulbs glow orange then red while cooling, and thus must be substantially cooled to avoid color shifts. After the strobe is discharged, the incandescent bulb must be restarted. It is well known that such restarts diminish the life of the bulb, and further that the start and stop latency may reduce productivity. Therefore, according to one aspect of the invention, the pilot lamp is provided as a short-persistence fluorescent bulb or metal vapor lamp, in which the pilot lamp is momentarily turned off, only for a short period, and therefore is not subject to substantial restart latency. For example, in a lamp with an alternating current drive circuit, the drive circuit may block current flow during a limited number of current cycles, while maintaining the bulb xe2x80x9cwarmed upxe2x80x9d during the hiatus.
In one example, a 50 Watt high pressure sodium vapor lamp is employed. Typically, the strobe illumination is on the order of up to one thousandth of a second, and is thus faster than the camera shutter. Mechanical shutter flash synchronization speeds range from about {fraction (1/75)} to {fraction (1/500)} second (2-15 mS). Typically, a high pressure sodium vapor lamp runs at 60 Hz, Therefore, the lamp may be turned off for as little as xc2xd to 1 cycle (9-18 mS). The cessation of illumination comes almost immediately after electrical power cutoff, since current flow rather than heat is the primary cause of light output. Practically, in order to assure strobe and shutter synchronization, as well as adequate decay of pilot light emission, a hiatus of 100-250 mS may be appropriate. In any case, this hiatus is short enough to allow rapid restart of the lamp with minimal warm-up delay. If necessary, color balance may be improved in the pilot light by providing a complementary lamp, such as a mercury vapor lamp, which may be controlled similarly to provide a mix of orange (sodium) and blue (mercury) pilot light and a hiatus during strobe.
In another case, the pilot lamp is distributed, with a source portion provided associated with each flash head. In this case, the pilot lamp may be, for example, a 5-25 watt fluorescent or halogen incandescent bulb. Since the pilot lamps are distributed, a means for equalizing light output is provided. The pilot light from a head should have an intensity that directly corresponds to the intensity of the flash associated with that head, in a predetermined ratio so that the pilot lights from all heads together may be judged together. While the intensity of a metal vapor or fluorescent lamp may be modulated (over a limited range) by altering a drive waveform, with less significant change in color output, incandescent lamps have a color that changes materially with change in output. Thus, an iris, shutter or filter is preferred to produce large variations in light output, which can be used to adjust both the pilot and flash intensity.
It is noted that, in many systems, the range of brightness modulation available for the pilot lamp is limited. Thus, both incandescent and fluorescent bulbs have a predefined operating point. In order to obtain a range of illumination intensities, a number of individual bulbs may be selected or xe2x80x9crecruitedxe2x80x9d to vary the overall illumination intensity while operating each element within its design parameters. Therefore, embodiments of the present invention may employ a number of separate pilot lamps which are individually controlled to produce a desired level of illumination, for example correlating to the selected power level of the flash lamp.
In order to normalize a distributed pilot lamp to the associated flash output, a calibration procedure is performed. Essentially, the calibration procedure seeks to assure a constant relation between the flash output and the pilot lamp output for each fiber optic head, thus allowing accurate surrogacy of the pilot during modeling and positioning. Preferably, each fiber optic head also has a normalized light output, but this is not required, since the light output of each head is preferably separately controllable at the discretion of the operator.
In one embodiment, an electronically adjustable pilot intensity control is provided to the pilot in each head. During a calibration phase, a light sensor measures the strobe output for each head under known conditions (e.g., 18% gray reflectance), and then adjusts the pilot to produce a fixed and equal percentage of the strobe output for that head. The direct light output to produce the calibration condition is then compared to the calibration level and a closed loop feedback control implemented to maintain the ratio over time and over varying environmental conditions. Each control may shut off the local pilot immediately before strobe exposure, and re-power the pilot thereafter, to the adjusted intensity level. In this way, it is also possible to control and normalize the intensity of the pilot to accurately represent the intensity of the flash.
The present invention preferably provides a plurality of strobe outputs having a consistent color temperature over a range of output levels. This allows variation in exposure without color temperature shift. It is well known that, in powering a strobe, use of pulse width modulation over a large range will vary the color output of the tube. In order to remedy this, it is preferred that the starting voltage on the capacitor for each flash discharge cycle within a set be equal. The intensity of the strobe may then be modulated by providing one or more strobe capacitors in parallel to alter the discharge power, and by limiting the light by use of filters, shutters or irises. Therefore, the time-normalized shape of the discharge pulse is maintained, thus balancing the color of the flash potentially over orders of magnitude of output.
Each flash head preferably also includes a mechanical iris or shutter to block portions of the flash and pilot light. This method, however, is inefficient and potentially reduces flash bulb life, and is therefore preferably provided primarily for fine adjustments and differential adjustments between the heads.
It is noted that color balance is more important between respective heads during an exposure or set of exposures than per an absolute standard. Thus, it is possible to provide various methods for modulating strobe output, so long as the same output is obtained from each source. It is also possible to intentionally provide variations in color from the various heads.
By providing equal color balance from each head, artifacts due to different color shadows are avoided. On the other hand, these artifacts may be intentionally applied if predictable.
An important aspect of various embodiments of the invention is the use of a fiber randomizer to ensure that fibers to each fiber optic head have a relatively uniform distribution with respect to variations in source characteristics, thus assuring uniform illumination to each fiber bundle in spite of variations at the particular location of the source fiber. Thus, while the many fibers may have significantly different illumination conditions, and thus have non-uniform light intensity, color, transmission mode, and other characteristics, once highly randomized, these bundles will have essentially matched characteristics.
In a preferred embodiment, the pilot lamp and flash lamp are housed together, with each fiber directed toward and receiving illumination from both lamps. This is possible because the flash lamp is transparent, and may be aligned with the filament of the incandescent lamp.
As discussed above, in one embodiment, both the pilot lamp and flash lamp are individually provided in each head. An electronic exposure control ensures that each pilot lamp output corresponds to the flash output, with electronic and/or mechanical control over the output of each head. If it is desired that each head have the same base output, this may be provided in various ways. For example, a small fiber or fiber bundle from each lamp may illuminate a common photothyristor. Each flash is triggered separately, for example at 0.5 mS intervals, to produce an identical output. The resulting illumination appears continuous, with few artifacts. Alternately, each head is provided with a separate photothyristor, each of which is calibrated to a common standard.
There are a number of advantages to distributed illumination, including scalability, economies of scale, and reduced need for long, flexible fiber optic cables. In fact, short illuminators may be provided as solid rod light pipes, liquid fiber optic conduits, and/or multiple fibers. Thus, the effects of a single illumination system may be synthesized while providing reduced size and cost standardized components.
Additionally, by providing the flash and pilot lamp closer to the point of use, higher optical efficiencies may be achieved. Thus, the combined outputs of the fiber optic heads may be substantially smaller than the corresponding output of a consolidated light source.
Another advantage accrues from distributed light sources, which is that electronic control over light output is facilitated. Thus, instead of expensive precision mechanical controls or quality optical filters, an electronic control system may be implemented to control light output. This, in turn, allows the mechanical or optical controls to be reduced or minimized. Further, the prospect of electronic control facilitates automation, especially where a predetermined lighting effect is or may be defined.
It is therefore an object of the invention to provide a fiber optic illumination system having multiple fiber optic heads wherein the light output of each head has a normalized relationship between pilot lamp output and strobe output over a range of strobe outputs. The color balance of the plurality of heads for at least a strobe illumination is preferably also normalized.
It is a further object of the invention to provide an illuminator having a continuous output illumination mode and a flash output illumination mode, wherein an illumination intensity ratio of continuous illumination and flash illumination is predefined over a range of flash illumination levels, wherein the illuminator is adapted to have its flash illumination synchronized with other like illuminators, and wherein a color balance of synchronized illuminators may be normalized over the range of flash illumination levels.
These and other objects will become apparent from a review of the Drawings and the Detailed Description of the Preferred Embodiments. For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.